P0378

What it means

P0378 is the generic code for an intermittent or erratic signal on the high resolution timing reference circuit 'B'. The engine control unit saw missing, irregular or noisy pulses on this signal that did not match what it expected from the engine's rotation. This high resolution signal is only fitted to certain engines, and which sensor or circuit counts as 'B' depends on the model and engine.

Symptoms

• Malfunction indicator lamp on
• Intermittent misfire or rough running
• Hesitation or hunting idle
• Occasional hard starting or long cranking
• Intermittent stalling
• Loss of power or poor fuel economy

Possible causes

• Damaged, chafed or corroded wiring or loose connector on the timing reference sensor circuitlikely
• Faulty timing reference or crank/cam position sensor producing erratic outputlikely
• Damaged, dirty or loose reluctor/tone wheel or trigger ring, or metal debris on the sensor tippossible
• Electrical interference from poor earths, a weak battery or low charging voltagepossible
• Incorrect sensor air gap or loose sensor mountingpossible
• Mechanical timing fault such as a stretched chain or jumped belt (model dependent)rare
• Faulty engine control unitrare

How to diagnose

1. Read all stored and pending codes and the freeze frame data, noting engine speed, load and temperature when the fault set, and check for related crank or cam sensor and misfire codes.
2. Check the battery condition and charging voltage, as low voltage during cranking can cause erratic signals.
3. Inspect the sensor wiring, connector and earths for chafing, heat damage, water ingress, corrosion and poor pin tension.
4. Wiggle-test the harness and connector with the engine running while watching live engine speed and sensor data for dropouts.
5. Check the sensor is secure, correctly seated and free of oil, debris or metal particles, and confirm the air gap where the model specifies one.
6. Inspect the reluctor or trigger wheel for damage, missing teeth, looseness or contamination where it can be accessed.
7. Check the sensor signal on an oscilloscope against the manufacturer's known-good pattern, and test the supply, signal and earth circuits for continuity and shorts.
8. Check the mechanical timing if the signal looks correct but the correlation is wrong, following the procedure for that engine.

How to fix

• Repair or replace damaged wiring and connectors, and clean or restore poor earths.
• Replace the faulty timing reference, crank or cam sensor once the circuit has been proven good.
• Replace or correctly refit a damaged or loose reluctor or trigger wheel, and clear any debris from the sensor area.
• Correct the battery or charging system fault if voltage is low or unstable.
• Correct the mechanical timing and replace worn components if that is found to be the cause.
• If all else checks out, confirm whether an ECU software update or ECU fault applies to that model before replacing the unit.

Can I keep driving?

Nearby codes

• P0377GenericTiming Reference High Resolution Signal B Too Few Pulses
• P0379GenericTiming Reference High Resolution Signal B No Pulses